The experiments outlined in this grant application are an extension of our pilot project to further study and evaluate the suppression of dimethylhydrazine (DMH) induced colon cancer in mice by a dietary supplement of various protease inhibitor preparations derived from soybeans. We have previously found that several different protease inhibitors have the ability to suppress the malignant transformation of C3H/10T1/2, A31-11 mouse BALB/3T3 and human diploid (AG-1522) cells in vitro, with inhibitors of chymotrypsin being the most potent of the protease inhibitors we have studied. The Bowman-Birk inhibitor from soybeans is a potent inhibitor of chymotrypsin activity. We have previously determined that this protease inhibitor very effectively suppresses the malignant transformation of cells treated with carcinogens, and, when ingested in the diet, reaches the colon in an active form. The animal experiments outlined in this proposal are designed to further study the ability of the Bowman-Birk inhibitor to suppress DMH-induced colon cancer in mice as follows: 1) We will perform a dose response experiment in which we will attempt to determine the lowest amount of a crude extract of the Bowman-Birk inhibitor in the diet which suppresses DMH induced colon cancer; the highest dose to be used in this study is that previously used for our pilot project utilizing a similar design to that proposed here. 2) We will chemically modify our crude inhibitor preparation such that most of the trypsin inhibitory activity is eliminated while the endogenous chymotrypsin inhibitory activity is left intact. We will evaluate the ability of this chemically modified, crude inhibitor preparation to inhibit DHM-induced colon cancer in mice in a dose dependent manner. 3) We will detemine the ability of the purified Bowman-Birk inhibitor from soybeans to suppress colon cancer in a dose dependent manner. 4) We will determine whether the three protease inhibitor preparations (crude inhibitor, succinylated crude inhibitor and pure Bowman Birk inhibitor) to be tested for their ability to suppress colon cancer have any adverse effects on the growth rates or the general health of treated animals, with particular emphasis being given to possible pancreatic changes. Before any protease inhibitor preparations are added to the diets of experimental animals, their protease inhibitory activity and their ability to suppress carcinogen induced transformation in C3H 10 T1/2 cells in vitro will be verified. The ultimate goal of our work is to design a dietary supplement consisting of a protease inhibitor preparation from soybeans which can be added to human diets and work as a non-toxic, colon cancer chemopreventive agent.